In the field of loudspeaker transducer types, planar magnetic devices, while having sonic attributes that are often heralded as advantageous and the basic forms of the device have been around for decades, have fallen far short of even 0.1% market penetration.
Planar magnetic devices may be classified as double-ended or push-pull devices and single-ended devices. Double-ended or push-pull devices comprise groups of magnet rows on both sides of a thin film diaphragm such that the magnets actively displace the diaphragm from two directions. Single-ended devices, on the other hand, comprise groups of magnets arranged on only one side of the diaphragm such that the magnets actively displace the diaphragm from only one direction.
Conventional double-ended or push-pull devices, because they have magnets on both sides of the diaphragm, have a variety of limitations. Those shortcomings include a reduced ability to reproduce high frequencies accurately without linear distortions due to cavity effects from magnet structures in front of the vibratable diaphragm. Additional structural problems are caused by repulsion forces between the front and back magnet structures, particularly when high energy magnets are used. High energy magnets in a double-ended arrangement require extensive bracing and/or heavy frame materials to inhibit flexing of the frame supporting the magnets. If the frame supporting the magnets flexes, the tension on the diaphragm can become unstable, resulting in distortion. A frame capable of rigidly supporting the magnets to prevent instability in the diaphragm tension can be costly structures. Conventional double-ended or push-pull devices thus are expensive and/or exhibit limited performance that fail to be competitive with conventional loudspeakers and can increase the aforementioned high frequency problem even further.
Single-ended devices have historically been large, energy inefficient devices with inefficient use of magnet material, requiring a multitude of magnet rows and large area diaphragms and magnet structures while still realizing substandard efficiencies. More recent single-ended devices such as U.S. Pat. No. 7,142,688 have attempted to use three or more rows of high-energy Neodymium magnets, but the three or more rows of strong interactive forces among the magnets cause a constant rolling force on the transducer frame structure that tends to deform the frame (e.g., buckle, curl, or “potato chip”). Buckling of the frame can cause the mounting distances of the film attachment to change, thereby altering the delicate tensioning of the film diaphragm and cause the diaphragm to be unstable and lose tension over time. As the diaphragm becomes unstable and loses tension, the dimensions of the magnetic gap change. Alteration of the tension of the diaphragm and/or changes in the magnetic gap can result in distortion of the sound, such as buzzing, and contributes to reliability problems. One approach to preventing deformation of the frame is to provide a heavier frame structure with complex bracing designed to hold the magnets, frame, and tensioned diaphragm in stasis, but a braced, heavier frame structure tends to be expensive to manufacture. A heavier frame structure also employs more frame material than what would otherwise be required to support efficient magnet coupling without saturation. Accordingly, singled ended devices also have historically not made the most efficient use of the amount of magnet material utilized. The increased structural stability requirements and poor magnet utilization can further increase cost. Also, the bracing elements that may be required to stabilize the frame structure can cause interference with the acoustic outputs due to reflections.
Conventional planar magnetic devices thus tend to be more costly than conventional dynamic loudspeakers. Conventional planar magnetic devices further require pluralities of rows of substantially equal energy magnets to reach practical levels of efficiency. And even the most efficient planar magnetic devices are less efficient than conventional dynamic loudspeaker systems. Additional limitations of prior art planar magnetic transducers have to do with mounting of the high-energy, high-magnet count structures and the associated cost and difficulty of assembly.
Still further limitations relate to reflections and standing waves that are due to film edge termination problems due to high, under-damped energy at the film termination points. Solutions to this have used mechanical damping of the film surface area and tend to be very lossy, causing further inefficiencies and limited use of the total diaphragm area.
Another problem with prior art planar magnetics is that, to make them large enough to have good dynamic range and output, such devices tend to have limited dispersion, resulting in substantially pistonic drive that tends to beam the sound at higher frequencies due to equal electromagnetic drive over the surface area.
It would be valuable to have a new device that can further improve on the sound quality of planar magnetic transducers while simplifying construction, lowering cost, maximizing the output while requiring fewer high-energy magnets and achieving performance to cost value that is superior to both conventional planar and conventional dynamic transducers.